I practice technical aspects of playing 30 minutes before I go to sleep every night. I play chromatics, scales, chords, sweeping, etc. The songwriting portion of playing I only do when I feel inspiration hits. This may be for 5 hours one day, or for two minutes another. Sometimes not at all.

30 minutes a day is good for people like me that are in high school, play sports, and have a job. Consistency is what counts.